Attention Deficit/Hyperactivity Disorder (ADHD) is characterized by symptoms of inattention, hyperactivity, and impulsivity. Deficits in inhibitory control and associated frontostriatal (FS) circuits have long been implicated in association with the disorder, but recent studies suggest that abnormal emotional processing within frontolimbic (FL) circuits may also be an important component of the hyperactivity evidenced in children with ADHD. Deficits in either domain may therefore be associated with ADHD and determine the clinical phenotype that a particular child exhibits. Using functional magnetic resonance imaging (fMRI), the current study aims to investigate simultaneously the functioning of FS and FL circuits in the same group of children as this is the best means to determine whether these two circuits have dissociable functions and neuropsychological correlates in children with ADHD. The study will examine in 60 children (ages 8 - 12) with (N=30) and without (N=30) ADHD the functioning of FS circuits during the performance of an inhibitory control fMRI task and the functioning of FL circuits during the performance of an emotion processing fMRI task. The hypotheses are that the functioning of these circuits will not only differ in children with and without ADHD but also that a double dissociation will be found in the behavioral correlates of FS and FL circuits. This application for a Mentored Patient-Oriented Research Career Development Award (K23) also requests funding for Jonathan Posner, MD to pursue training essential to becoming an independent investigator. This funding would support a comprehensive program including formal didactics and seminars from experts in the fields of pediatric neuroimaging, cognitive and affective neuroscience, and pediatric psychopathology. These training activities would enhance Dr. Posner's knowledge of a) fMRI techniques; b) the pathophysiology, phenomenology, and treatment of ADHD, c) affective and cognitive neuroscience; d) longitudinal neuroimaging study design; and e) the ethical conduct of scientific research.